RFR: 8341982: Simplify JButton/bug4323121.java [v5]

[Alexey Ivanov]

On Fri, 18 Oct 2024 22:36:33 GMT, Sergey Bylokhov <serb at openjdk.org> wrote:

>> This test follows the same pattern that I used in https://github.com/openjdk/jdk/pull/21474:
>> 
>> https://github.com/openjdk/jdk/pull/21474/files#diff-2a8cee50408407d7e24de4cb85f0921cfc5db7c215d3b29cf101a4050323e9a9R92
>
>> To ensure all the events in the queue are handled, I added `robot.waitForIdle()`.
> 
> This will flush events which were posted after the windows gained focus, but before the patch the test flushed all events (including event to show the window which might be asynchronous). My point is that this operation might be longer that 1 second(one of the reason we have all that deleyas). So we should waitForIdle first, then wait via delay or other sync_ops.

This will flush all the pending events in the queue, which includes events that were posted before the `windowGainedFocus` latch is released as well as events are posted afterwards.

There's no difference whether I place `waitForIdle` before or after.

If I place `robot.waitForIdle` before `windowGainedFocus.await`, then `await` immediately returns, that is the delay added by `await` is zero.

If I place `robot.waitForIdle` after `windowGainedFocus.await`, the main thread stops until the window gained focus event is delivered, after which `robot.waitForIdle` flushes the remaining events in the queue.

In both cases, there's a slight possibility `windowGainedFocus` is never triggered if the window didn't get focus for whatever reason…

On my Windows 11 laptop, the average time (over 20 runs of the `bug4323121` test)

* for `windowGainedFocus.await`: 12 ms
* for `robot.waitForIdle`: 36 ms
* or cumulatively: 48 ms

If I change the order of calls,

* for `robot.waitForIdle`: 51 ms
* for `windowGainedFocus.await`: 0 ms
* or cumulatively: 51 ms

Both versions align well — `robot.waitForIdle` takes about 50 ms. (The version where `waitForIdle` follows `await` is slightly quicker because `await` does nothing at all whereas `waitForIdle` posts events from its own copy of the queue for handling.

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PR Review Comment: https://git.openjdk.org/jdk/pull/21475#discussion_r1809317633